From: Thomas Zimmermann Date: Tue, 2 Dec 2025 20:23:12 +0000 (-0500) Subject: drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup X-Git-Tag: v6.12.61~7 X-Git-Url: http://git.ipfire.org/cgi-bin/gitweb.cgi?a=commitdiff_plain;h=482330f8261b4bea8146d9bd69c1199e5dfcbb5c;p=thirdparty%2Fkernel%2Fstable.git drm, fbcon, vga_switcheroo: Avoid race condition in fbcon setup [ Upstream commit eb76d0f5553575599561010f24c277cc5b31d003 ] Protect vga_switcheroo_client_fb_set() with console lock. Avoids OOB access in fbcon_remap_all(). Without holding the console lock the call races with switching outputs. VGA switcheroo calls fbcon_remap_all() when switching clients. The fbcon function uses struct fb_info.node, which is set by register_framebuffer(). As the fb-helper code currently sets up VGA switcheroo before registering the framebuffer, the value of node is -1 and therefore not a legal value. For example, fbcon uses the value within set_con2fb_map() [1] as an index into an array. Moving vga_switcheroo_client_fb_set() after register_framebuffer() can result in VGA switching that does not switch fbcon correctly. Therefore move vga_switcheroo_client_fb_set() under fbcon_fb_registered(), which already holds the console lock. Fbdev calls fbcon_fb_registered() from within register_framebuffer(). Serializes the helper with VGA switcheroo's call to fbcon_remap_all(). Although vga_switcheroo_client_fb_set() takes an instance of struct fb_info as parameter, it really only needs the contained fbcon state. Moving the call to fbcon initialization is therefore cleaner than before. Only amdgpu, i915, nouveau and radeon support vga_switcheroo. For all other drivers, this change does nothing. Signed-off-by: Thomas Zimmermann Link: https://elixir.bootlin.com/linux/v6.17/source/drivers/video/fbdev/core/fbcon.c#L2942 # [1] Fixes: 6a9ee8af344e ("vga_switcheroo: initial implementation (v15)") Acked-by: Javier Martinez Canillas Acked-by: Alex Deucher Cc: dri-devel@lists.freedesktop.org Cc: nouveau@lists.freedesktop.org Cc: amd-gfx@lists.freedesktop.org Cc: linux-fbdev@vger.kernel.org Cc: # v2.6.34+ Link: https://patch.msgid.link/20251105161549.98836-1-tzimmermann@suse.de Signed-off-by: Sasha Levin Signed-off-by: Greg Kroah-Hartman --- diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c index b15ddbd65e7b5..a8971c4eb9f05 100644 --- a/drivers/gpu/drm/drm_fb_helper.c +++ b/drivers/gpu/drm/drm_fb_helper.c @@ -30,9 +30,7 @@ #define pr_fmt(fmt) KBUILD_MODNAME ": " fmt #include -#include #include -#include #include #include @@ -1637,10 +1635,6 @@ static int drm_fb_helper_single_fb_probe(struct drm_fb_helper *fb_helper) strcpy(fb_helper->fb->comm, "[fbcon]"); - /* Set the fb info for vgaswitcheroo clients. Does nothing otherwise. */ - if (dev_is_pci(dev->dev)) - vga_switcheroo_client_fb_set(to_pci_dev(dev->dev), fb_helper->info); - return 0; } diff --git a/drivers/gpu/drm/i915/display/intel_fbdev.c b/drivers/gpu/drm/i915/display/intel_fbdev.c index 49a1ac4f54919..337cc9fc31b19 100644 --- a/drivers/gpu/drm/i915/display/intel_fbdev.c +++ b/drivers/gpu/drm/i915/display/intel_fbdev.c @@ -589,11 +589,8 @@ static int intel_fbdev_restore_mode(struct drm_i915_private *dev_priv) static void intel_fbdev_client_unregister(struct drm_client_dev *client) { struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); - struct drm_device *dev = fb_helper->dev; - struct pci_dev *pdev = to_pci_dev(dev->dev); if (fb_helper->info) { - vga_switcheroo_client_fb_set(pdev, NULL); drm_fb_helper_unregister_info(fb_helper); } else { drm_fb_helper_unprepare(fb_helper); @@ -620,7 +617,6 @@ static int intel_fbdev_client_hotplug(struct drm_client_dev *client) { struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); struct drm_device *dev = client->dev; - struct pci_dev *pdev = to_pci_dev(dev->dev); int ret; if (dev->fb_helper) @@ -634,8 +630,6 @@ static int intel_fbdev_client_hotplug(struct drm_client_dev *client) if (ret) goto err_drm_fb_helper_fini; - vga_switcheroo_client_fb_set(pdev, fb_helper->info); - return 0; err_drm_fb_helper_fini: diff --git a/drivers/gpu/drm/radeon/radeon_fbdev.c b/drivers/gpu/drm/radeon/radeon_fbdev.c index fb70de29545c6..a197ba2f2717b 100644 --- a/drivers/gpu/drm/radeon/radeon_fbdev.c +++ b/drivers/gpu/drm/radeon/radeon_fbdev.c @@ -300,10 +300,8 @@ static void radeon_fbdev_client_unregister(struct drm_client_dev *client) { struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); struct drm_device *dev = fb_helper->dev; - struct radeon_device *rdev = dev->dev_private; if (fb_helper->info) { - vga_switcheroo_client_fb_set(rdev->pdev, NULL); drm_helper_force_disable_all(dev); drm_fb_helper_unregister_info(fb_helper); } else { @@ -325,7 +323,6 @@ static int radeon_fbdev_client_hotplug(struct drm_client_dev *client) { struct drm_fb_helper *fb_helper = drm_fb_helper_from_client(client); struct drm_device *dev = client->dev; - struct radeon_device *rdev = dev->dev_private; int ret; if (dev->fb_helper) @@ -342,8 +339,6 @@ static int radeon_fbdev_client_hotplug(struct drm_client_dev *client) if (ret) goto err_drm_fb_helper_fini; - vga_switcheroo_client_fb_set(rdev->pdev, fb_helper->info); - return 0; err_drm_fb_helper_fini: diff --git a/drivers/video/fbdev/core/fbcon.c b/drivers/video/fbdev/core/fbcon.c index 1fc1e47ae2b49..e681066736dea 100644 --- a/drivers/video/fbdev/core/fbcon.c +++ b/drivers/video/fbdev/core/fbcon.c @@ -65,6 +65,7 @@ #include #include #include +#include #include #include #include @@ -77,6 +78,7 @@ #include #include /* For counting font checksums */ #include +#include #include #include "fbcon.h" @@ -2894,6 +2896,9 @@ void fbcon_fb_unregistered(struct fb_info *info) console_lock(); + if (info->device && dev_is_pci(info->device)) + vga_switcheroo_client_fb_set(to_pci_dev(info->device), NULL); + fbcon_registered_fb[info->node] = NULL; fbcon_num_registered_fb--; @@ -3027,6 +3032,10 @@ static int do_fb_registered(struct fb_info *info) } } + /* Set the fb info for vga_switcheroo clients. Does nothing otherwise. */ + if (info->device && dev_is_pci(info->device)) + vga_switcheroo_client_fb_set(to_pci_dev(info->device), info); + return ret; }